The MBTI Is Not Science — It's Astrology With Four Letters

In 1943, two women with no formal psychology training published a personality test based on Carl Jung’s theoretical book Psychological Types. Katharine Cook Briggs and her daughter Isabel Briggs Myers were not psychologists, had never conducted empirical research, and had no academic affiliation. They were simply fascinated by Jung’s ideas and wanted to make them useful. Today, that test — the Myers-Briggs Type Indicator — is used by 22 percent of employers in the United States to screen candidates, determine promotions, and assign team roles. The gap between the MBTI’s origin story and its influence in HR is not a minor oversight. It is a category error. Companies treat the MBTI as a diagnostic instrument when it was never validated as one. The American Psychological Association has long described the necessary conditions for a credible personality test as a three-legged stool: reliability (does it produce consistent results?), validity (does it measure what it claims to measure?), and fairness (does it treat groups equitably?). The MBTI fails the first two legs consistently. Test-retest studies show that as many as half of people who take the MBTI are assigned a different type when they retake it weeks later. A test that cannot agree with itself cannot tell you anything stable about a candidate. The research community reached this conclusion decades ago. In 1991, a National Academy of Sciences review found the MBTI had “no demonstrated predictive validity” for job performance. The alternative that dominates academic personality psychology — the Big Five model (Openness, Conscientiousness, Extraversion, Agreeableness, Neuroticism) — emerged from factor analysis of natural language descriptors, not from a single theorist’s untested typology. The Big Five shows strong test-retest reliability, cross-cultural replicability, and modest but real predictive power for workplace outcomes. The MBTI shows none of these properties. Yet the MBTI persists, and the reason is instructive. In 1948, psychologist Bertram Forer gave his students a personality description composed entirely of vague, flattering statements — “You have a great need for other people to like and admire you,” “You pride yourself as an independent thinker” — and asked them to rate its accuracy. The average rating was 4.26 out of 5. This became known as the Barnum effect: people accept generic positive descriptions as uniquely personal insights. The MBTI’s output — four letters that feel like a secret identity — is a Barnum statement dressed in institutional credibility. It feels true because it is flattering and ambiguous, not because it is accurate. The harm is not merely intellectual. When a hiring manager treats an MBTI type as a fixed trait, they introduce a classification bias that has no empirical warrant. A candidate who tests as “Introverted” on one occasion may be excluded from client-facing roles. A team leader who believes their type is “rational” may dismiss input from colleagues whose type they perceive as “emotional.” The test creates categories and then treats those categories as real, when in fact the underlying data — the distribution of human personality — is continuous, context-dependent, and poorly captured by four binary switches. The most widely used personality test in business is closer to astrology than to science. That is not an opinion. It is the documented conclusion of every major review conducted over the past thirty years. If you have been categorized by an MBTI assessment at work, the label says far more about the history of the test’s creation than it does about you.